The present invention generally relates to a bar code reading apparatus, and more particularly to a bar code reading apparatus capable of precisely reading a bar code even when it is printed on a wrapper or the like with a positional error so that a margin area preceding or following the bar code is less than a predetermined width.
Conventionally, a bar code reading apparatus is used in a point-of-sales system. The bar code reading apparatus reads bar codes attached to wrappers of goods or the like. As is known, it is necessary to precisely recognize margin areas provided before and after the bar code and thereby read the bar code without errors.
A conventional bar code reading apparatus scans a bar code by a scanner and determines whether a margin area (normally a "white" area) is equal to or greater than a predetermined width (generally equal to seven modules). Such a bar code reading apparatus is disclosed in U.S. Pat. No. 4,074,852.
As shown in FIGS. 1A and 1B there is no problem when the conventional bar code reading apparatus scans a margin area which is equal to or greater than a predetermined width W1. It is noted that the last character bar is followed by guard bars, which are followed by the margin area. A low level of the illustrated signal indicates "white", and a black level thereof indicates "black". In contract, the conventional bar code reading apparatus cannot read bar codes precisely in a case where as shown in FIG. 1B, a bar code is printed in a rectangular white area surrounded by a black area (margin defining area or black frame) so that a margin area before or after the bar code is less than the predetermined width W1 (in the illustrated case, a back margin area after the guard bars has a width W2 less than the predetermined width W1). A similar problem may occur in a case where a front portion and/or a back portion itself of a bar code is curved, a bar code label attached on a wrapper is warped due to the presence a good contained therein.